The invention relates to an internal combustion engine comprising a compressor including an impeller and an electric motor for driving the impeller and to a method for operating an internal combustion engine.
A turbocharger for an internal combustion engine which comprises a compressor in the intake line and an exhaust gas turbine in the exhaust gas line is described in the publication DE 692 19 822 T2. Herein, the turbine wheel is coupled to the compressor impeller in a rotationally fixed manner by a shaft, so that the rotation of the turbine wheel generated by means of the exhaust gases of the internal combustion engine is also transmitted to the compressor impeller. The compressor then compresses combustion air from the environment to an elevated charging pressure. The exhaust gas turbocharger also includes an electric motor, by means of which the charger can additionally be driven electrically in certain operating phases. The electric motor comprises a stator fixed to the housing and a rotor arranged in a rotationally fixed manner on the shaft in the region between turbine wheel and compressor impeller.
DE 199 55 508 C1 discloses an exhaust gas turbocharger for an internal combustion engine having a compressor with a housing which includes, parallel to an axial compressor inlet duct in which the compressor impeller is rotatably mounted, an additional duct which opens into the compressor inlet duct at the level of the compressor impeller. Combustion air can be supplied to the compressor impeller both via the compressor inlet duct and via the additional duct. The path via the additional duct is selected in particular in low load and low speed operating states of the internal combustion engine. With the low pressure which prevails in these operating states in the region of the cylinder inlets of the internal combustion engine, a pressure drop exists across the compressor which makes flow via the additional duct and the compressor impeller possible even without external drive of the compressor impeller. The combustion air supplied via the additional duct meets the compressor impeller blades radially and imparts a driving torque to the impeller. At low loads and speeds, the compressor can consequently be operated like a turbine (cold-air turbine operation). This mode of operation makes it possible to maintain a minimum speed level of the exhaust gas turbocharger in all operating states of the internal combustion engine.
A supercharged internal combustion engine with an exhaust gas turbocharger and an additional compressor in the intake line is also known from DE 102 21 014 A1. The compressor of the exhaust gas turbocharger has an additional duct which extends parallel to the compressor inlet duct and opens into the compressor inlet duct at the level of the compressor impeller blades. An actuator allows the air supply to be set axially via the compressor inlet duct to the compressor impeller and also radially via the additional duct to the compressor impeller blades. The shaft of the exhaust gas turbocharger can also be driven directly by means of an electric motor.
It is the object of the present invention to overcome the problem of keeping the compressor impeller speed at a minimum level with low energy expenditure. In particular when a compressor is used in an internal combustion engine, it is to be ensured on one hand that a minimum speed of the compressor is maintained during no-load operation and in the lower part-load range of the internal combustion engine and, on the other hand, that charge air is made available with the smallest possible time delay for rapid acceleration of the engine.